THE DETERMINATION OF THE SHAPE OF DEVELOPING CORROSION PITS

A simple numerical method was developed to calculate the shape and size of growing corrosion pits. It was shown that the surface of a closed pit, growing under mass-transfer control in the absence of convection, can be described with the help of a general expression which depends only on the initial geometry of the system but not on its physical properties. For sufficiently large times they can be approximated by the equation by an ellipsoid of revolution. The growth of open and closed corrosion pits on iron in 1 M NaCl was simulated in case the current density at their surface is determined by a Tafel kinetic expression. The shape of these pits depends on their initial form and on a possible supersaturation of the system. Numerical calculations are compared with published experimental data.